Pharmaceutical tablets and other confectionary compressed tablet forms are very common and widely accepted delivery vehicles for pharmaceutical actives or powders. They provide a convenient means to compress a relatively large volume of low density powders into a smaller compact format that is easily handled, swallowed, or chewed. Various shapes, sizes, and configurations are common in the marketplace. The vast majority of these tablet forms are manufactured from dry blends of compressible powders or granulations that are then fed into rotary tablet compression machines (e.g., such as those commercially available from Fette America Inc., Rockaway, N.J. or Manesty Machines LTD, Liverpool, UK). These tablet compression machines accurately dose a predefined amount of powder into a die cavity. The powder is then compressed using punches which impinge upon the powder and compact it within the die cavity. The final step in the operation is to eject the finished tablet form from the die cavity completing the manufacturing sequence. Most tablet constructions made from this process are simple single component forms; however these machines can sometimes be modified to produce more complex multi-layer tablets by adding multiple feeding and compression stations. Multi-layer tablets produced by this means are procedure in a sequential and stepwise fashion whereby layers or sections are built up layer upon layer. Each layer requires an additional dosing assembly punches and an additional compression assembly. Since these machines have a relatively massive construction due to the very high compaction forces required to get formulations to compact properly (machines capable of producing up to 20,000 pounds force are quite common) multi-layer machines can become very expensive and hard to maintain. An additional drawback to producing tablets in this fashion is the limitations of the layered geometry. Regions of a tablet with an orientation that is perpendicular to the tablet ejection direction are extremely hard to produce and would require more elaborate and complex modifications.
A further drawback to the layer upon sequence of tablet manufacturing is specific to the production of orally disintegrating tablets. These tablets require a low density and highly porous tablet construction whereby saliva of the mouth quickly penetrates the tablet to break down the particle bonds to create a fast dissolve effect. The layer upon layer approach requires that a first layer of powdered material is first filled into a die cavity with the surface of the die cavity being scraped to establish the required volume of fill. This first fill layer is then compressed with a punch to a controlled depth of penetration into the die cavity. This depth of penetration must be precisely controlled and the powder must be uniformly compacted to create a controlled volume for the second fill of powder material. The next step of the operation is to fill this newly created volume with a second powder. This powder is then scraped flush with top surface of the die cavity and the final step is to compact the second layer upon the first layer a second time with a punch which presses upon both layers of the tablet. This double compaction smashes the tiny air pockets between particles causing a detrimental effect to the porous structure that is desired for the orally disintegrating tablet. In pharmaceutical manufacturing it is not possible to skip this double compression step because a dense uniform first layer is a prerequisite to achieving accurate dosing of the powdered medicament of the second layer. Accurate dosing of drugs by pharmaceutical manufacturers is critical to maintaining the health and safety of patients.